求助：用 Uikit 建一个瀑布流时第一个 box 异常显示

[atlantismonk]

HMTL:

<div class="uk-grid uk-flex uk-flex-item-auto">
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#5d925b;">Box1Box1Box1Box1Box1Box1Box1</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box"       style="background:#345233;">Box2Box2Box2Box2Box2Box2Box2Box2Box2Box2Box2Box2Box2Box2</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#893742;">Box3Box3Box3Box3Box3Box3Box3Box3Box3Box3</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#cc1133;">Box4</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#1a4344;">Box5</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#443f14;">Box6</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#244424;">Box7</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#0e0d44;">Box8</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#441520;">Box10</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#442429;">Box11</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#345233;">Box12</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#893742;">Box13</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#cc1133;">Box14</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#1a4344;">Box15</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#443f14;">Box16</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#244424;">Box17</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#0e0d44;">Box18</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#2f440e;">Box19</div></div>
        <div class=" uk-grid-medium " ><div class="uk-panel uk-panel-box" style="background:#441520;">Box20</div></div>
    </div>

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![Alt test][flex photo]
![Alt test][box1]
![Alt test][box8]

<img src="/home/atlantismonk/桌面 /flex_photo.png">
<img src="/home/atlantismonk/桌面 /box1.png">
<img src="/home/atlantismonk/桌面 /box8.png">

想试试用 Uikit 的 flex 和网格做瀑布流的 demo 遇到了个问题， box2-box20 的高度都是 50px ， box1 的高度却是 75px ，如果把 box1 删掉 box2 的高度就会是 75px 。

后来发现.uk_grid:before 选择器的高度是 75px （不过.uk_grid:before 选择器并没对 height 设置值），不知有什么关系。

求高手帮忙解答解答。