frontend: initial file component

frontend/src/lib/components/add_button.svelte

@@ -8,7 +8,7 @@
     <label for="img-upload" class="plus round" style="height: 48px; display: inline-block;">+</label>
     <input id="img-upload" accept="image/png, image/jpeg" style="display: none" bind:files type="file"/>
 {:else}
-    TODO
+    <button class="file-plus rounded" onclick={handler}>Загрузить файл</button>
 {/if}
 
 <style>
@@ -22,12 +22,30 @@
         align-content: center;
     }
 
+    .file-plus {
+        font-family: Arial, Helvetica, sans-serif;
+        font-size: x-large;
+        cursor: pointer;
+        text-align: center;
+        align-content: center;
+        width: 100%;
+        margin: 0;
+        height: 3rem;
+        border: 0.15rem dashed;
+    }
+
     @media (prefers-color-scheme: light) {
         .plus {
             background-color: #5C8DC0;
             color: white;
         }
 
+        .file-plus {
+            background: none;
+            border-color: #5C8DC0;
+            color: #5C8DC0;
+        }
+
         .plus:hover {
             background-color: #567aa1;
         }
@@ -39,6 +57,12 @@
             color: white;
         }
 
+        .file-plus {
+            background: none;
+            border-color: #2791FF;
+            color: #2791FF;
+        }
+
         .plus:hover {
             background-color: #2c7dd4;
         }